In LARP (“Laser Activated Remote Phosphor”) arrangements, at least one laser generates primary light that is converted at least partly into secondary light of a different wavelength by means of a wavelength-converting phosphor volume. The mixed light resulting from the secondary light and, if appropriate, a portion of the primary light that is not converted but is scattered by the phosphor volume can be used as useful light. By way of example, white useful light can be generated from a mixture of blue primary light and yellow secondary light. If, in the case of a transmissive arrangement, the phosphor volume is damaged in the region of the incident primary light beam, disadvantageously coherent primary light can pass through the phosphor volume and possibly not comply with predefined limit values with regard to eye safety. On account of the type of stimulating source (laser), often even a small degree of damage to the phosphor volume should be rated as critical for the purposes of eye safety. When a case of damage is identified, the laser generating the primary light can be deactivated or the primary light can be switched off.
In order to be able to identify damage to the phosphor volume, it is known to employ a relationship of exciting and transmitted power of the primary light and also a power of the secondary light. If, in this case, with constant exciting power, the transmitted power of the primary light increases and the power of the secondary light decreases, damage to the phosphor volume is assumed. One disadvantage of this method consists in the high outlay for the measurement set-up, e.g. owing to a high number of light sensors required. Moreover, the calibration, measurement data recording and the measurement data evaluation are complex. Furthermore, a higher reliability of the detection of the fault case or case of damage is desired. Particularly a detection when there is only a small change in the powers is not always possible without errors, since a laser power in the spectral range of the primary light is transmitted in normal operation as well.
DE 20 2015 001 682 U1 discloses an illumination device for a vehicle including a laser diode arrangement, a light wavelength conversion element for wavelength conversion of the light generated by the laser diode arrangement, and also a safety device for measuring a fault case of the light wavelength conversion element, wherein the safety device comprises at least one signal generator and at least one signal receiver for transmitting and receiving measurement radiation, wherein the at least one signal generator and the at least one signal receiver are arranged on different sides of the light wavelength conversion element, such that measurement radiation from the at least one signal generator penetrates through the light wavelength conversion element.